This invention is generally directed to conductive developer compositions, and processes for the preparation of toner and developer compositions. More specifically, the present Invention is directed to developers with certain conductivities. In one embodiment of the present invention, the developer comprises rough surfaced carrier components, or cores. There is also provided in accordance with the present Invention processes for the preparation of conductive developers containing toner compositions comprised of resin particles, pigment particles, and optional surface additives such as colloidal silicas, metal salts, metal salts of fatty acids, or mixtures thereof. The present invention is also directed to conductive developer compositions comprised of the aforementioned toners and ferrite carrier particles, reference for example U.S. Pat. Nos. 4,598,034 and 4,614,698, the disclosures of which are totally incorporated herein by reference, with rough surfaces thereon. The toner and developer compositions of the present invention are useful in electrophotographic imaging and printing systems, especially those systems wherein blade cleaning of the photoconductive member is accomplished. Further, the developer compositions of the present invention possess stable conductivities, that is for example the developer conductivity changes by a factor of three or less over a toner concentration range as large as 6 weight percent with nominal 100 micron average diameter carriers. For example, in one embodiment of the present invention the conductivity of the developer composition is from about 10.sup.-6 to about 10.sup.-12, and more specifically 6.times.10.sup.10 to about 3.times.10.sup.-10 (ohm-cm).sup.-1 for a corresponding toner concentration range of from 1 weight percent to about 6 weight percent.
Conductive xerographic developers containing either a positive or a negative toner polarity are useful in electrophotography, especially in xerographic imaging processes since, for example, such developers provide a higher degree of toner development than insulative developers. This increased degree of development allows the construction of compact machine designs, and/or provides for increased rates of copy generation. Conductive developers are especially useful in applications where large areas of extensive development are required, that is for example wherein large solid areas of text or pictorial renditions, either in black or color, are to be formulated. Also, conductive developers are usually characterized by the avoidance of the development of unwanted background particles (for example, the absence of toner particles in the white, non-image areas of copies), thus enabling images that typically evidence dark images on a pure white background. Conduction in a conductive xerographic developer refers to electrical conduction from carrier to carrier particle, and a developer will remain conductive when a carrier to carrier pathway is maintained. With use, conductive carrier particles may become coated with insulating material such as firmly-adhering toner particles or fragments, thereby resulting in the loss of conductive properties. Similarly, free, or triboelectrically held toner particles may disrupt carrier to carrier contacts, and thus reduce a conductive developer to an insulative failed state. The probability of this latter type of failure occuring will increase as the toner concentration of the developer increases, thus a developer which is conductive at a reasonable range of toner concentration will show an insulative failure if the toner concentration is allowed to increase to high values, that is where the surface of the carrier beads are substantially covered with toner particles. Further, conductive developers can also fail by becoming excessively conductive when, for example, they conduct a current of about 0.1 mA (milliamp) or more, and this type of failure is often associated with conductive developers based on metallic carriers. For the aforementioned carriers, the intrinsic conductivity of the metal is too high for many xerographic applications. These metallic carriers, therefore, are normally provided with a surface oxidation treatment, and/or a partial surface coating with an insulating polymer to reduce the metal conductivity to a lower useful level. Unfortunately, with use in xerographic machines, such protective carrier coatings or oxide layers are removed resulting in an eventual excessive conductivity failure state. Thus, there is a continued need for conductive developer designs with a conductivity not affected by carrier surface wear or contamination, and not affected by variations in toner concentrations over a certain range. These and other needs are accomplished with the present invention.
Stable conductive developer compositions are disclosed in U.S. Pat. No. 4,513,074, the disclosure of which is totally incorporated herein by reference. In this patent, there is disclosed stable conductive developers containing resin particles, pigment particles, colloidal silica additive particles, fatty acid metal salt additive particles, and uncoated ferrite carrier particles, reference for example the Abstract of the Disclosure. Conductive and other characteristics of the developer of this patent are illustrated, for example, in column 5, beginning at line 40. In column 4, lines 53 to 54, it is indicated that the carrier for the developer has a conductivity of from about 10.sup.-9 to about 10.sup.-12 (ohm-cm).sup.-1.
There is disclosed in U.S. Pat. No. 4,598,034 low density disintegrated ferrite carriers, however, there is no teaching in this patent relating to processes for obtaining stable developer conductivity over a wide range of toner concentration, although carrier conductivity is disclosed. More specifically, this patent is primary concerned with useful compositions of Cu-Zn.sup.- ferrites, see for example columns 2 and 3, and the working examples. Also, there is disclosed in U.S. Pat. No. 4,614,698 two component developers with magnetic carriers with certain parameters including an electrical resistance of from 6.times.10.sup.4 to 2.5.times.10.sup.6 ohms. In column 4 of this patent, it is indicated that ordinary ferrite carriers have a certain higher dynamic resistance. Also, in column 6, beginning at line 41, of the '698 patent it is indicated that the sintered ferrite particles have an uneven surface, or a fine uneven surface as a carrier component, see column 6, lines 47 to 48, for example. Further, in this patent there is also disclosed the effect of toner concentration on developer conductivity, and an optimum value of toner concentration is specified, see for example column 11, lines 20 through 68, and column 12, lines 1 through 9. Also, there is no teaching in this patent relating to maintaining the carrier conductivity over a wide range of toner concentrations by, for example, including a metal salt of a fatty acid in the toner, and selecting a rough surfaced carrier particle. Patents of background interest include U.S. Pat. Nos. 4,282,302; 4,407,923; 4,592,988 and 4,698,289.
Also, many patents disclose the use of metal salts of fatty acids, such as zinc stearate for toner compositions, such as U.S. Patent No. 3,655,374, the disclosure of which is totally incorporated herein by reference. Also, it is known that the aforementioned toner compositions with metal salts of fatty acids can be selected for electrostatic imaging methods wherein blade cleaning of the photoreceptor is accomplished, reference U.S. Pat. No. 3,635,704, the disclosure of which is totally incorporated herein by reference. Additionally, there are illustrated in U.S. Pat. No. 983,045, the disclosure of which is totally incorporated herein by reference, three component developer compositions comprising toner particles, a friction reducing material, and a finely divided nonsmearable abrasive material, reference column 4, beginning at line 31. Examples of friction reducing materials include saturated or unsaturated, substituted or unsubstituted, fatty acids preferably of from 8 to 35 carbon atoms, or metal salts of such fatty acids; fatty alcohols corresponding to said acids; mono and polyhydric alcohol esters of said acids and corresponding amides; polyethylene glycols and methoxy-polyethylene glycols; terephthalic acids; and the like, reference column 7, lines 13 to 43.